Production of nuclear fuel is often costly and complicated due to the amount of precautionary steps that are required to be undertaken during production of the fuel. In order to produce a safe nuclear fuel, nuclear fuel rods are designed with several different components, each of the components having a specific technical purpose. The innermost component is generally a uranium enriched ceramic material that is shaped in the form of a pellet. Individual pellets are placed end to end in a column. The pellets are then placed inside an elongated rod made of corrosion resistant metal called a fuel clad. The nuclear fuel pellets are loaded into the fuel clad generally according to several technologies. The uranium enriched ceramic material is protected from mechanical and chemical wear by the fuel clad during operation of the reactor. When originally fabricated, the nuclear fuel clad is open (unsealed) at the two ends of the rod. A first lower end piece can be welded onto the clad. The clad is then filled with the nuclear fuel pellets. Lastly, an upper end piece is welded to the remaining open end of the fuel clad thereby forming a completed fuel rod. As a precaution, springs and/or other devices are also included inside the volume encapsulated by the fuel clad to allow the uranium fuel pellets to swell and shift within prescribed limits in the fuel clad. Each completed fuel rod is then stored by the fuel rod manufacturer. A multitude of completed fuel rods are then configured in a parallel arrangement separated by fuel assembly spacers to prevent the fuel rods from contacting each other during use to form a fuel assembly.
The technologies currently used to incorporate the nuclear fuel pellets into the fuel clad have several drawbacks and are therefore not economically efficient. Due to the sensitive nature of the components involved, the production of nuclear fuel rods requires quality assurance checks to ensure that defects do not occur during the production of the nuclear fuel rods. To eliminate human error, many systems and technologies attempt to use automated systems to eliminate worker involvement in the process. Although well intentioned, the automated systems must be carefully designed such that during fabrication of the fuel rod, no loose pieces and/or parts are generated which will jam the machine and stop production. The creation of these automated systems is extremely complicated and the systems created are prone to error due to the inability of designers to accurately predict the failure modes and problems encountered during production of the fuel rods.
In current automated loading systems, nuclear fuel pellets are taken from a fuel pellet elevator and transferred by a conveyor to a segment make-up table. The pellets are loaded and discharged from the fuel pellet elevator with the assistance of a bar code reader which restricts entry and exit of the nuclear fuel pellets from the fuel pellet elevator. The fuel pellets are removed from the fuel pellet tray which carries the pellets and placed on a segment make-up table. The fuel pellets are placed in a parallel orientation and then compacted by a pusher device to form columns of uranium containing ceramic material. The pushing device is connected to a linear variable differential transformer which is configured to provide an electrical output signal. The signal is then read and an overall length of the individual fuel pellet column is determined. A computer then compares an overall design specification for the fuel rod with the output signal obtained from the linear variable differential transformer. If the difference between the expected design value of the nuclear fuel pellet column length and the measured value meets a predetermined threshold value, the fuel rod cladding is then loaded with the nuclear pellet column. If the overall length of the fuel pellet column is outside of the threshold value, the fuel pellets are then rejected from the segment make-up table. A top end cap is then welded the existing open side of the fuel rod cladding thereby completing the nuclear fuel rod.
The automated systems which only use linear variable differential transformers cannot identify damaged fuel pellets which are positioned on the segment make-up table. These automated systems merely check for an overall length of the nuclear material to be incorporated into the clad and do not perform any other quality assurance checks during fabrication of the nuclear fuel rod. Thus, if an individual nuclear fuel pellet is cracked, the cracked fuel pellets will be loaded into the nuclear fuel rod as long as the overall length of the expected nuclear fuel pellet column is within established design parameters. In the case of an irregular shaped fuel pellet, as long as the overall length of the fuel pellet column is within expected overall length parameters, the cracked fuel pellet will be incorporated into the nuclear fuel rod cladding. If the fuel pellet is of an irregular shape, the pellet will bind on the tightly fitting clad and therefore jam the loading operations. An operator must then remove the nuclear fuel pellets from the segment make-up table. The loading apparatus must then be reset and a new fuel tray must be provided to the segment make-up table in order for production of nuclear fuel rods to continue. The unloading of the multiple nuclear fuel pellets from the segment make-up table while in a jammed condition requires numerous manual operations thereby stopping production of nuclear fuel rods. This jamming impedes the overall production capacity of the segment make-up device and severely limits productivity.
An additional drawback of other fuel pellet loading systems is that these systems require continual fine tuning of the linear variable differential transformer systems in order to accurately measure the lengths of the nuclear fuel pellet columns present on the segment make-up table. Large numbers of the linear variable differential transformers are required for the fuel pellet columns on the segment make-up table to provide an accurate measurement of the fuel pellet columns present. There is therefore a need to provide a system which will accurately measure nuclear fuel pellet columns present on a segment make-up table.
There is also a need to provide an apparatus and method which will enable an operator to perform additional quality assurance checks of the nuclear fuel pellets during the manufacturing process of a nuclear fuel rod.
There is a further need to provide an apparatus and method which will allow for incorporation of ceramic materials inside nuclear fuel rod cladding such that the ceramic material is not harmed during the process of incorporating the ceramic materials into the fuel rod cladding.
There is a further need to allow an operator to visually determine which fuel pellets should be included into a defined segment of nuclear fuel rod material such that the incorporation does not degrade the ceramic materials being incorporated into the fuel rod cladding.